Uranium is a naturally occurring element which is comprised of approximately 0.7% .sup.235 U and 99.3% .sup.238 U. .sup.235 U is used to produce Nuclear Energy, while .sup.238 U is not. Because of the low percentage of .sup.235 U found in naturally occurring uranium, naturally occurring uranium must be enriched in order to obtain sufficient amounts of .sup.235 U to support nuclear fission. This enrichment process, aside from producing high concentrations of .sup.235 U, produces huge amounts of depleted uranium hexafluoride (UF.sub.6) by-product which is a very hazardous compound posing a serious health threat. Since depleted uranium metal is radioactive and expensive to produce, it is used in limited quantities for highly specialized applications. Accordingly, alternative uses are needed in order to avoid having to dispose of the UF.sub.6 at great expense by storing it indefinitely. One solution to reducing the large stores of UF.sub.6 is to convert the UF.sub.6 into uranium oxide, e.g. UO.sub.2 or U.sub.3 O.sub.8.
One use for uranium oxide is to add it to the concrete which is used to build bunkers in which radioactive waste is stored in order to provide high density shielding for the stored high level radioactive waste. Uranium oxide possesses outstanding radioactive shielding properties and when added to concrete in the form of aggregate makes a very effective, low cost shielding material.
There are many methods which can be used to convert UF.sub.6 into uranium oxide. Many of these methods also produce potentially valuable by-products. However, methods which are currently used to convert the UF.sub.6 into uranium oxide taint these valuable by-products with radioactive uranium, rendering the by-products commercially unusable, requiring additional processing to remove the radioactivity, as well as additional contaminants, or disposing of the by-products as low level radioactive waste.
The most common method for producing uranium oxide includes reacting uranium hexafluoride with steam (H.sub.2 O) and hydrogen (H.sub.2). This produces uranium oxide and hydrogen fluoride gas (HF). However, because the products and reactants are mixed in the gas phase, this HF gas, although having economic value, is contaminated by unreacted uranium thus reducing its value as discussed above. Also, this HF gas is highly diluted from addition or excess amounts of steam.
Another method for producing uranium oxide reacts UF.sub.6 with H.sub.2 to produce uranium tetrafluoride (UF.sub.4) and HF gas. The UF.sub.4 is then reacted with steam to produce a uranium oxide, UO.sub.2 or U.sub.3 O.sub.8, and HF gas. However, the reverse reaction is so strong that tremendous amounts of steam must be used to avoid a reverse reaction. This not only requires a large amount of energy to produce the steam, but again produces a highly diluted hydrogen fluoride product that has little commercial value, requiring further processing to obtain a valuable product. Moreover, complete conversion to uranium oxide is nearly impossible thereby degrading the uranium oxide's suitability for making concrete and thus the value of the uranium oxide produced.
Accordingly, the major drawbacks of the presently preferred methods are that the HF is diluted and contaminated with some amount of uranium making it commercially unusable. Thus, while HF has some economic value, the uranium contamination reduces this value and further provides yet another storage dilemma, as encountered with all radioactive waste, or additional processing to purify the HF.
Moreover, these methods are very expensive. Thus, an economical way to convert UF.sub.6 to uranium oxide is needed in order to make use of the large quantities of UF.sub.6 in storage and produce commercially valuable by-products which are not radioactive and require no additional processing.